1. Field of the Invention
The present technology relates to a secondary battery protection circuit, a secondary battery protection device, a battery pack and a method of writing data.
2. Description of the Related Art
Conventionally, a secondary battery protection circuit for protecting the secondary battery is known (for example, see Patent Document 1). In FIG. 2 in Patent Document 1, a battery pack is disclosed, which includes a flash ROM and a voltage step-up circuit for generating a voltage to write data in the flash ROM. According to Patent Document 1, the voltage step-up circuit is disposed inside the battery pack since the voltage to write data in the flash ROM needs to be greater than the voltage to power the flash ROM. However, area of a chip may become greater due to the voltage step-up circuit, therefore a method for improving chip size reduction is also disclosed.
A specification of the secondary battery protection circuit needs to be customized in accordance with types of the secondary battery or a product in which the secondary battery protection circuit is installed. If a configuration of the secondary battery protection circuit is designed on a type-by-type basis of the secondary battery or the product so as to adapt the secondary battery protection circuit to discrete specifications, a lead time and a cost for development are likely to increase.
Therefore, a design for adapting a common circuit configuration to discrete specifications is proposed, in which a memory for recording data such as respective parameters for defining the specification is disposed and the specification is set based on the parameter data retrieved from the memory. According to the aforementioned design, the specification can be changed in the common circuit configuration by changing the parameter data recorded in the memory. For example, in a case where a voltage value to be set as an overcharge detection voltage, which is included in the specification, is recorded in the memory, the value of the overcharge detection voltage can be changed in the common circuit configuration by changing the set voltage value.
The respective parameters are an overcharge detection threshold voltage, an overcurrent detection threshold voltage, a short-circuiting detection threshold voltage, delay times for performing the respective detections corresponding to the respective threshold voltages, and so on. Also, in a case where trimming is performed so as to absorb dispersion (manufacture irregularity) of the respective threshold voltage, the trimming data is also recorded in the memory.
Meanwhile, in order to write the parameter data for defining the specification of the secondary battery protection circuit in a nonvolatile memory, a voltage greater than an operational voltage (a normal power supply voltage) of the secondary battery protection circuit and the nonvolatile memory is required to be supplied to the nonvolatile memory. Therefore, any of methods can be adopted, in which the power supply voltage is stepped up to generate the voltage to write the data or in which a designated terminal for receiving the voltage to write the data from an external device is provided. However, the area of the chip will increase due to the step-up circuit when adopting the former, and a total number of terminals in the secondary battery protection circuit will increase upon adding the designated terminal for receiving the voltage to write the data to the secondary battery protection circuit when adopting the latter.